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Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>

8.3 Treatment (Topic c)

The Pacific has been described as a "junk yard" of water sector technologies with failed systems spread throughout the Region. Developed country technologies have been superimposed on the Region with less then successful results mainly due to the lack of sustainable resources for on going operation and maintenance. A SOPAC organised Regional workshop on Appropriate and Affordable Sanitation for Small Islands was held in Kiribati in 1996. It became clear from the workshop that sanitation involves more than just physical structures for excreta disposal. Health and hygiene education is also regarded as important aspects for any proposed sanitation project. Also community involvement and participation is most important to have a successful project. The production of the SOPAC publication Guidelines for Selection and Development for Small Islands (see reference 3) was a result of the Kiribati workshop.

SOPAC has also produced guidelines on Small Scale Wastewater Treatment Plant (see reference 8) that focuses on SIDS. These are further discussed in Section 8.3.1 below.

Previous American influenced countries in the Region (American Samoa, FSM, Guam, Mariana Islands, Marshall Islands and Palau) have some sort of wastewater reticulation system and primary to secondary treatment for their main urban centres. However the standard of effluent produced ranges from raw sewage from Marshall Islands to good quality from Guam and American Samoa. All these countries discharge their wastewater into coastal areas.

Apart from the major urban centres in Fiji, PNG, Kiribati, New Caledonia and the Solomon Islands, plus the above mentioned American influenced countries, the balance of the Regions communities use septic tanks, various types of latrines and over water latrines. Composting toilets have been introduced and trialed in some SIDS including Kiribati, FSM, Fiji and Samoa. (See Case study 2) The bush, beach and the sea are still used for defecation in many places, (Figure 8.1)

Open Defecation

Where there are no latrines people resort to defecation in the open. This may be indiscriminate or in special places for defecation generally accepted by the community, such as defecation fields, rubbish and manure heaps, or under trees. Open defecation encourages flies which spread faeces-related diseases. In moist ground the larvae of intestinal worms develop, and faeces and larvae may be carried by people and animals. Surface water run-off from places where people have defecated results in water pollution. In view of the health hazards created and the degradation of the environment, open defecation should not be tolerated in villages and other builtup areas. There are better options available that confine excreta in such a way that the cycle of reinfection from excreta-related diseases is broken.

Figure 8.1: Open Defecation

In the Greenpeace Pacific publication, Sewage Pollution in the Pacific and How to Prevent It,1996 (see references) they state that human excreta is a resource that should be recovered and reused, rather than disposed of into the marine environment. They also state that limited water resources should not be used to convey wastes. They support non-water-carried ecologically engineered treatment systems that use natural processes to convert excrement into usable fertiliser and soil conditioner. Where it is not practical to convert existing conventional treatment systems, Greenpeace recommends that industrial waste and disinfection by chlorination be prohibited in domestic wastewater systems.

Greepeace recommends that the following criteria be used in the selection of technologies for managing human and domestic wastes:

  • Achieve zero discharge
  • Recover excreta as a resource
  • Avoid the use of water
  • Prohibit industrial wastes and disinfection with chlorine

In addition significant reductions in pollution discharges from existing conventional treatment systems are recommended by:

  • Water conservation
  • Use of sludge generated by treatment plants
  • Wastewater reuse
  • Supplementary treatment using ecologically engineered technologies

Waterless composting toilets meet all Greenpeace criteria. They are being trailed and used in parts of Kiribati, the Federates States of Micronesia, and Fiji indicating good potential. Composting toilets are best suited for individual households, but are considered to have limited applications in urban conditions.

8.3.1 Small-scale and community technologies

Septic tanks and various types of latrines are exclusively used in the Cook Islands, Niue, Tokelau, Tonga, Tuvalu, Vanuatu and Samoa but are used throughout the Region as well. These methods are mainly for individual family and household use. Some communities (in PNG and Kosrae) use large septic tanks along with some schools and hospitals for wastewater treatment and disposal. Appendix 2 shows various types sanitation systems plus constraints and advantages used in the Region.

UNESCO/SOPAC trials were carried in Tonga to assess what the safe distance between shallow wells and household "toilet" discharges. The study found that most wells used for the study were already polluted. The results were inconclusive suggesting that the minimum distance should be as far apart as possible.

In Yap (FSM) an Imhoff tank is use to treat wastewater. The utility reports that there is a big demand for the dried sludge taken from the Imhoff tank.

Section 8.5.2 discusses land base wastewater disposal in more detail.

Oxidation ponds only appear to be used in Fiji, PNG and Kosrae. Pond treatment methods generally do suit atoll conditions where land is very limited and ground conditions very permeable results in expansive implementation.

There are still circumstances where individual on-site treatment and/or conventional sewage treatment systems may not offer the best solution to deal with shallow groundwater and coastal water pollution problems. Thus guidelines have been developed by SOPAC to use Small Scale Wastewater Treatment Plant (SSWTP) technologies that may be applied where:

  • Conventional sewage treatment systems are too expensive.
  • Environmental conditions require a higher quality effluent.
  • Conventional on-site treatment may have a low community acceptance.
  • Low technology solutions, such as the composting toilets, may be inappropriate.

The guidelines give technical criteria for the selection of appropriate wastewater treatment technologies, suggesting a rating scheme to assist in making a choice. For each of the six criteria, there are rating choices of low, moderate and high or a simple yes, no. The procedure is to work through the criteria, rating each, based on the particular circumstances facing the community or group of households. The assessed criteria ratings are then compared to a list of sound technologies that have been evaluated on the same criteria. The likely suitable technologies quickly become apparent. As an example under the criteria of "Electrical Requirement" if no electricity is available the rating given will be no, and then technologies requiring electrical equipment drop out. The various criteria and ratings follows:

  • Effluent Quality:
    Where health and environmental risks are a major concern, then a better effluent quality may be required. However if the under lying groundwater for example is not considered as a useable resource, then the discharge quality may not need to be of high quality.
  • Water Supply: (Yes or No)
    Most SSWTP would require a reliable water supply to convey waste to the treatment plant and to the discharge point. If water were not available then technologies selections would be fewer. In some cases seawater may be used if freshwater is limited.
  • Land Space: (Low, Moderate or High)
    In many SIDS, land is in customary ownership and land use is a very sensitive issue. Some treatment processes require large areas which often is not readily available.
  • Maintenance and Operation: (Low, Moderate or High)
    All treatment systems require some degree of maintenance to keep them operating satisfactorily. Many treatment processes require high levels of trained personnel and good supply of spare parts. This is not available in most island applications.
  • Cost: (Low, Moderate or High)
    Affordability is often a constraint to providing adequate waste disposal within the Pacific Region. However governments and/or external donors fund many waste disposal schemes. In these cases the users need to be able to pay for the operation and maintenance of the system.
  • Electrical Requirement: (Yes or No)
    If no electrical power is available then selection is again limited. Without power this virtually eliminates the use of any pumping to convey, treat and dispose of wastewater. In some cases, low tech turbine or "water ram" driven pumping systems can still be used.

The following technology rating list should be use as a guide to selecting a suitable technology:

Technology Criteria
Process Types
 
Effluent
Quality
Water
Land
O & M
Cost
Electricity
Primary Treatment
Composting
Toilets
Composting Toilets, Enviroloo, Soltrann II Low No Low Low Low No
Composting
Toilets
Composting Toilets, Nature-Loo, Rota-Loo, Biolet Low No Low Low Low Yes
Septic Tank
Usage
Septic Tank to disposal field Low Yes Low Low Low No
  Septic Tank with up-flow filter Moderate Yes Low Low Moderate No
  Imhoff Tanks Low Yes Low Low Low No
Septic Tanks Baffled Septic Tanks Moderate Yes Low Moderate Low No
Ponds/Lagoons/
Tanks
Small Anaerobic Ponds treating domestic wastewater Low Yes Moderate Low Moderate No
  High loaded Anaerobic Ponds with long HRT Moderate Yes Moderate Low Moderate No
  Low loaded Anaerobic Ponds with short HRT Low Yes Moderate Low Moderate No
  Low loaded Anaerobic Ponds with long HRT High Yes Moderate Low Moderate No
  Low loaded Sedimentation Tanks with short HRT Low Yes Moderate Low Moderate No
  Low loaded Sedimentation Tanks with long HRT High Yes Moderate Low Moderate No
Secondary Treatment
Land Treatment Slow Rate Process Moderate Yes High Low Moderate No
  Overland Flow Process Moderate Yes High Low Moderate No
  Rapid Infiltration Treatment Process High Yes High Low Moderate No
Ponds/Beds Reed Bed System (SSF)
Subsurface Flow Wetlands/Root Zone TP/Horizontal Gravel Filter
High Yes Moderate Moderate Moderate No
  Aerobic Stabilisation Ponds/ Oxidation Ponds/Algal Ponds High Yes High Low Moderate No
Filters Anaerobic Filters Moderate Yes Low High High Yes
  Trickling Filters/Percolating Filter High Yes Moderate Moderate High Yes
Activated
Sludge
Activated Sludge Treatment High Yes Low High High Yes
Tertiary Treatment
Hybrid Systems Hybrid Toilet Systems (T\HTS) High No Low Moderate Moderate Yes
Package Plant
Types
N-DN Biofilter Treatment Plants High Yes Low High High Yes
Package Plant
Types
Enviroflow Biofilter Treatment Plant Systems High Yes Low High High Yes
Package Plant
Types
Cromaglass Unit High Yes Low High High Yes
Package Plant
Types
Intermittent Decanted Extended Aeration System (IDEA) High Yes Low High High Yes
  Tertiary Lagoons High Yes High Low Moderate No
  BanksEClarifiers High Yes High Low Moderate No
  Grass Plots / Wetlands High Yes High Low Moderate No
Source: SOPAC (1999) Small Scale Wastewater Treatment Plant Project Report on Criteria, Guidelines and Technology by Bower and Scholzel.

Note that the "package plants" above are considered tertiary if they are used as a polishing process of treated effluent.
The table ratings were done from the available information. It can be seen from the different ratings that each technology has its strong and weak points and therefore an effective combination of these treatment technologies together would maximise the meeting of the criteria.

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